Comparison of the effect of dopamine in primate arteries and veins

Mechanical responses to dopamine of isolated human and monkey veins were isometrically measured and compared to those of the arteries. Human gastroepiploic and monkey mesenteric veins responded to dopamine with contractions, whereas the arteries in the same region responded with relaxations. Treatment with phentolamine converted the venous contraction to a relaxation, which was not influenced by propranolol but was abolished by droperidol. The relaxation was endothelium-independent and converted to a contraction by SCH23390 but unaltered by domperidone. Dopamine increased the cyclic AMP content in the human veins. Monkey vena cava and portal vein did not respond to dopamine with relaxation even under alpha-adrenoceptor blockade. It is concluded that primate veins and arteries from the gastric and mesenteric regions respond quite differently to dopamine; the alpha-adrenoceptor-mediated contraction predominates over the relaxation mediated via D1-receptor in the veins, and vice versa in the arteries. In monkey large veins, dopamine receptor does not appear to play a functional role. The veno-constrictor action of dopamine, together with actions on myocardium and resistance vessels, would contribute to increasing of the cardiac output.